1. Field of the Invention
The invention is directed to methods and composition of using organic molecules termed pro-NAD agents capable of enhancing dermal and epidermal skin cell NAD content with a resulting enhancement of DNA repair and other protective responses to genotoxic stress in skin.
2. Description of the Background
The present application relates to methods and compositions capable of modulating and upregulating the cellular nicotinamide-adenine-dinucleotide (NAD) content by the topical application of chemical agents for the purpose of enhancing natural protective responses of skin cells to DNA damage. The methods and compositions are effective for the prevention and treatment of skin deterioration that results from DNA damage to cells of the skin. The symptoms of such skin deterioration are many and typically include the loss of moisture, fine lines, deep lines, wrinkles, and loss of elasticity as well as atrophic sclerosis and other blemishes of skin. Skin deteriorates with age as a natural consequence of prolonged exposure to internal and external factors. Internal deterioration factors include natural metabolic byproducts such as free radicals which cause the aging of all tissues. External deterioration factors include ionizing radiation such as sunlight and chemical insults such as pollution and cigarette smoke. In theory, skin care methods and compositions should inhibit, or slow the process of skin deterioration by counteracting these internal and external factors. Unfortunately, current methods and compositions for skin care are generally reactive rather than proactive. That is, current methods and compositions reduce or obscure the signs of aging but have minimal or no effect on the underlying progressive and cumulative biochemical processes that cause skin deterioration. It is therefore desirable to have a skin care method and composition which not only reduce the symptoms of deterioration but also treat the underlying causes of skin deterioration in such a way that deterioration can actually be retarded. To understand the limitations of current methods and compositions, it is necessary to understand the function and structure of the skin and the mechanisms of skin deterioration.
At ten pounds, the skin is the largest organ in the body. FIG. 1 shows a diagram of skin marking the location of the two major cell types present in skin, namely fibroblasts located in the dermal layer of the skin and keratinocytes located in the epidermal layer of the skin. The skin provides the first line of defense between the body's interior and harmful environmental insults by well established physical and biochemical mechanisms. Physical protection mechanisms include the relatively impermeable barrier the skin provides. The skin can, to some extent, repel and absorb insults such as chemicals and ultraviolet light so that while the skin may be damaged, the underlying tissue is preserved. Biochemical mechanisms include the innate and acquired immune systems. Microbiological pathogens are repelled by immune responses at the epidermal level involving Langerhans cells, keratinocytes, cytokines, polynuclear cells, endothelial cells, mast cells, and lymphocytes.
Structurally, the skin comprises epithelial tissue (the epidermis) in the outer layer and beneath it, connective tissue (the dermis), and beneath that, the fatty tissue (hypodermis). The epidermis is not vascularized and regenerates every four to six weeks. Its primary function is to maintain the body's skin integrity, acting as a physical barrier to toxic agents, dirt, bacteria, microorganisms, and physical insults. The dermis is beneath the epidermis and functions by providing strength, support, blood, and oxygen to the skin. The principal cell components of the dermis are fibroblasts although it also contains sweat glands, sebaceous glands, hair follicles, and small fat cells. Hypodermis, also known as the superficial fascia, attaches the dermis to the underlaying structures. Its function is to promote an ongoing blood supply to the dermis for regeneration.
The mechanisms of skin deterioration involve a gradual and progressive process that beings from birth. Internal factors that contribute to skin aging include toxic metabolic byproducts, autoimmune diseases, and genetic predisposition. The consequences of internal deterioration can be observed over the entire body from the skin to the internal organs. While the mechanisms of internal deterioration are not completely understood, somatic mutation has been shown to be a contributing factor. Under the somatic mutation theory, cells gradually lose their youthful characteristics and their capacity to divide by the accumulation of mutations (errors) in their genetic code. These mutations may be caused by free radicals or alkylating agents generated in metabolism that lead to unrepaired DNA damage. Over time, mutations accumulate in the body until the cell can no longer divide or produce functional proteins.
External factors such as chemical and physical agents in the environment can also cause DNA damage that leads to skin deterioration. The external factors include sunlight, pollution, and ingested chemicals from smoking or from food.
Deterioration of skin leads to changes in dermal thickness and elasticity due to increased crosslinking of collagen. Epidermal regeneration increases in activity while metabolism, sweat glands, and vascularization, all decrease in activity. The damage from internal and external factors is progressive and cumulative and results in the appearance of deterioration associated with aged skin.
Related to the somatic mutation theory, both internal and external factors contribute to oxidative stress, which in turn results in DNA damage. In humans, oxidative stress and DNA damage is caused by factors such as hyperbaric oxygen, gamma radiation, ultraviolet radiation, ozone, peroxides, free radicals, alkylating agents, and redox cycling drugs. While total oxidative stress and DNA damage may be reduced by living in a low pollution environment and avoiding sunlight, they cannot be eliminated. Some factors like ionizing radiation are present in all environments at a low level and other factors are byproducts of metabolism and cannot be totally eliminated. Further, urban environments have high levels of ground level pollution from a variety of sources that are not likely to be reduced in the near future. However, while DNA damage cannot be avoided, not all DNA damage leads to mutations.
DNA damage does not necessarily lead to mutation because a normal cell contains diverse and effective systems for repairing damaged DNA. There are at least 50, and possibly more than 100 genes involved in DNA repair. The importance of good DNA repair in retarding skin deterioration is most noticeable in patients that suffer from DNA repair defects such as xeroderma pigmentosum (XP). XP have early and accelerated skin deterioration, clearly demonstrating the importance of DNA repair to reducing deterioration of the skin. In addition to DNA repair, a normal cell also has systems that invoke “programmed cell death” by a process termed apoptosis. The process of apoptosis effectively “erases” cells damaged beyond the point of repair. These natural defense mechanisms of the skin have been ignored by current methods of preventing skin deterioration.
Many creams, lotions, bath oils, ointments, pastes, cleansers, covers, and powders claim to be effective in preventing skin deterioration. However, all current methods and compositions have severe disadvantages in that they are limited in their ability to retard skin deterioration. Most over the counter skin care products soften deteriorated skin or otherwise reduce the symptoms of deteriorated skin with no effect on the underlying biochemical processes involved in deterioration. Many existing skin care products and cosmetics function by providing moisture to the skin, preventing moisture loss, or providing cover to obscure the visible signs of deterioration. While traditional cosmetics may have effects on appearance, these effects are evanescent and any apparent improvement disappears as soon as the product use is discontinued. Further, traditional cosmetics' effectiveness decrease upon exposure to moisture and thus cosmetics must be reapplied after exercise, swimming, or any other exposure to moisture. Some cosmetics contain metals (e.g., iron and copper) which may actually increase skin levels of free radical formation and possibly promote deterioration. As the use of such products does not prevent deterioration, more and more of the product is needed as time progresses to obscure the increasing severe condition of the underlying skin.
Another method for treating aging skin is the use of alpha hydroxy acids (AHA) such as lactic acid, citric acid, glycolic acid, malic acids; beta hydroxy acids (BHA) such as salicylic acid; and retinoids (e.g. tretinoin (retin A), retinol and retinal), as exfoliants. These agents help remove the uppermost layer of skin to expose the more youthful underlying skin. However, there is a danger that by removing the outer layer of skin, AHA, BHA and retinoids can compromise the important barrier function of skin. It is possible that the use of these exfoliants may accelerate skin aging by removing the protective outer layer of skin. Exfoliants and other ingredients may also increase the skin's sensitivity to environmental conditions such as sunlight, wind, cold temperature and dry air, or to chemical agents such as antigens, or may exacerbate the irritation attributable to a pre-existing skin disease. Another disadvantage of AHA, BHA and retinoids is that these compounds are potential skin irritants which can induce side effects such as sore, red skin.
Another popular method for skin treatment is the use of sunblocks. Sunblock (i.e., sunscreen) refers to any chemical that when applied to the skin, reduces the amount of UV light that reaches the skin. By preventing UV absorptions that cause genomic mutations, sunblocks can decrease and retard skin deterioration. Sunblocks were originally designed to prevent sunburn (also known as erythema), an acute reaction to overexposure to the sun. The strength of sunblocks is measured by the SPF index (Sun Protection Factor). An SPF value of 15, for example, will provide 15 times the protection of bare skin to sunburns. However, it should be noted that the SPF values, which measures resistance to sunburn, cannot be extrapolated to photoaging protection, which is caused by constant low level environmental insults. That is, a sunblock with an SPF factor of 15 will not reduce photoaging 15 fold. There is also a danger that chemicals in some sunblocks will increase DNA damage and contribute to skin deterioration. Finally, every major class of sunblock has been linked to skin allergies.
Finally, there are agents that are physical blends of existing agents. A physical blend is a mixture of two or more chemicals. Physical blends can be mixed powders, mixed solutions, mixed emulsions, mixed colloidal solutions, particles in solutions, and the like. An example of a physical blend may be a covering or coloring cosmetic mixed with a sunblock (titanium dioxide) and a hydroxy acid.
In summary, current methods of skin treatment are mostly reactive in that they treat the symptoms of deterioration after the damage is done. Current skin treatment methods do not reverse damage to the dermal tissue. There is a need for topical skin care products that are proactive rather than reactive. A proactive product is one that will assist the skin in resisting DNA damage by either preventing damage or assisting in repair of any damage.